GB2257509A

GB2257509A - Multiple beam transit document detector for printer

Info

Publication number: GB2257509A
Application number: GB9212770A
Authority: GB
Inventors: Paavo Perala; Rauno Repo
Original assignee: ICL Personal Systems Oy
Current assignee: ICL Personal Systems Oy
Priority date: 1991-06-24
Filing date: 1992-06-16
Publication date: 1993-01-13
Anticipated expiration: 2012-06-16
Also published as: JPH05221557A; ITTO920537A1; GB9212770D0; ES2070034A2; FI88134B; ES2070034R; ES2070034B1; JP3051573B2; FI913078A0; DE4219548C2; DE4219548A1; FI88134C; IT1259593B; ITTO920537A0; GB2257509B

Description

225) 7_ ú j I,- 1 A printer or a similar output device This invention

relates to a printer or a similar output device for producing characters on a document fed into a paper transfer passage of the device, comprising at least one means provided in connection with the paper transfer detecting the document, said means passage for comprising a photoemitter and a photodetector positioned in the paper transfer passage so that a document fed to a light propagation path between the photoemitter and the photodetector causes a change in the amount of light received by the photodetector.

Conventional printers used in banking, for instance, utilize photoelectric components for detecting the presence of a document. Such components can be used in several ways, typically in three dif ferent ways. First, it is possible to provide a light source, such as a LED emitting infrared light, at the bottom of the paper transfer passage, and a phototransistor at a corresponding point on the upper surface of the paper transfer passage for detecting the light emitted by the LED when no hindrance, i.e. no document, is positioned between the LED and the phototransistor. The second basic principle is to position both the source of light and the photodetector at the bottom of the paper transfer passage, so that the light is caused to propagate between them when a document with a reflective lower surface is brought above them. The third basic principle is to position both the photoemitter and the photodetector similarly as above, i.e. at the'bottom of the paper transfer passage, whereas they are continuously connected with each other through a means reflecting the light beam, such as a prism, positioned on the upper 2 surface of the paper transfer passage. In this case, the connection between the photoemitter and the photodetector is broken when a document is fed into the paper transfer passage. The above-described spotlike detectors are typically provided at the edge of the paper transfer passage in the vicinity of an edge guide. When using this kind of printer, the document has to be positioned against the edge guide, and so it suffices that the document detector is positioned in the vicinity of the edge guide. In such a case, the presence of the document in the paper transfer passage can be detected by a single spot- like detector.

To detect whether the document is straight the paper transfer passage, that is, whether its back edge is at right angles to the longitudinal direction of the paper transfer passage, more advanced structures based on the above-mentioned basic detectors are used, in which two detectors of the type described above are positioned on the same line, which is at right angles to the longitudinal direction of the paper transfer passage. When only one of these detectors indicates that the document is in the paper transfer passage, one knows that the document is not straight. On the contrary, when both detectors detect the presence of the document, one knows that the document is straight. This, of course, requires that the line on which the detectors are positioned is right at a back edge guide for the document. The purpose of the back edge guide is to ensure that the document is straight before it is fed into the paper transfer passage.

In printers where the feeding of the document is allowed practically at any transverse position of the paper transfer passage, that is, it need not be 1 -1 3 positioned against the side edge guide, the document can, of coiirse, also be detected by using detectors of the type described above, provided that a sufficient number of detectors are positioned on a line extending transversely across the paper transfer passage. A problem therewith is, however, that the signals of several photoemitters and particularly several photodetectors have to be observed simultaneously. Although it is easy to obverse several photodetectors simultaneously, it increases, with conventional solutions, the demand of wiring and complicates the detection equipment itself. These factors also have importance in view of the competitiveness of the product in printers which are intended for mass production and which should also be as small as possible.

The object of the present invention is to provide a printer or a similar output device in which the feeding of a document into the paper transfer passage is allowed at any transverse position of the paper transfer passage, while the detection of the document, however, is carried out very simply. A printer or a similar out-out device according to the invention by means of which the object is achieved is characterized in that optical means are provided on the light propagation path between the photoemitter and the photodetector, said optical means being positioned on the opposite surfaces of the paper transfer passage with a mutual spacing in the transverse direction of the paper transfer passage so as to cause the light to pass several times across the paper transfer passage before it falls on the photodetector.

In cases where it is to be monitored whether the document is at right angles to the paper transfer 01 4 passage, so that the photodetectors have to be positioned in -pairs, the printer or a similar output device according to the invention is characterized in that optical means are provided on the light propagation paths between the photoemitter(s) and the photodetectors, said optical means being positioned on the opposite surfaces of the paper transfer passage so as to cause the light to pass several times across the paper transfer passage before it falls on the photodetectors.

Preferably the optical means comprises a prism or a length of an optical f ibre in the shape of an arch so as to divert the light beam so that it is again passed across the paper transfer passage from a point spaced from the inlet point in the transverse direction of the paper transfer passage.

In a preferred embodiment, the optical means used to determine whether the document is at right angles is a prism comprising two light inlets and two light outlets, thus forming part of both light propagation paths.

In the following the printer or a similar output device according to the invention will be described in greater detail with reference to the attached drawing, in which Figure 1 illustrates the way according to the invention for detecting a document in the paper transfer passage of a printer; Figure 2 illustrates the way according to the invention for connecting photodetectors so as to operate in pairs for detecting whether a document is at right angles; and Figure 3 illustrates another embodiment of the optical means to be used with the procedure shown in Figure 2.

Figure 1 shows an optical means positioned in a paper transfer passage 1 of a printer so that a document (not shown) fed to a light propagation path between a photoemitter Ul and a photodetector Ql causes a change in the signal received by the photodetector Ql when the document is fed substan tially at any transverse position of the paper trans fer passage. This property is achieved by causing the light beam to propagate several times between the upper and lower surfaces of the paper transfer passage 1 from points spaced apart from each other in the transverse direction of the paper transfer passage by using optical means 2. In the embodiment of Figure 1, the optical means 2 comprise prisms which first receive the light beam and then refract it so that it propagates in the transverse direction of the paper transfer passage 1 before they again pass it across the paper transfer passage from another point. By dimensioning the prisms in a desired manner, a desired number of points with desired spacings are achieved, from which the light beam is passed across the paper transfer passage. By suitable dimensioning of the prisms 2, such points can be provided with spacings such that a document equal to or greater than the smallest allowable document will always be detected reliably. Even though the prisms 2 in the embodiment of Figure 1 refract the light beam so that it propagates perpendicularly across the paper transfer passage 1, it is also possible to re- fract the light beams so that they propagate obliquely across the paper transfer passage, in which case it would be possible to make the optical means simpler in structure. At simplest, mere reflective mirror surfaces could be used to pass the light beam over the paper transfer passage in the transverse 6 direction along a zigzag-like path from the photoemitter to the photodetector. A problem therewith would, however, be the provision of light beams of a sufficiently narrow beam. This property is improved in the embodiment of Figure 1 by providing optical masks 9 in front of both the optical means 2 and the photoemitter Ul and the photodetector Ql on both surfaces of the paper transfer passage, the optical masks allowing the passage of light therethrough only in narrow beams. In this way the detection is made as position sensitive as possible, and the disturbing effect of light falling on the detector from the environment is avoided. The effect of the environment can be further reduced by modulating the light emitted by the photoemitter in a desired manner.

By means of the arrangement shown in Figure 1, the entire paper transfer passage can be monitored, if desired, by means of a single photoemitter and a single photodetector. However, it is possible, especially in cases where the paper transfer passage is relatively broad, to provide several such arrangements as shown in Figure 1 side by side in the transverse direction of the paper transfer passage. A reason for this is mainly that the intensity of the light signal decreases over its propagation path to such an extent that it cannot any longer be detected reliably.

In Figure 1, the optical means 2 is shown to be formed by a prism, which is very simple to manufac- ture of e.g. a plastic material by casting. So the cost of such a prism is very low; in practice, it is substantially lower than the cost -of an individual photoemitter or photodetector. In addition, the dimensions of this kind of cast body can be made very accurate; such bodies can also be easily provided 7 with projections and the like to facilitate the installation. Alternatively, the optical means shown in Figure 3 can be used in place of the prism of Figure 1. The optical means of Figure 3 comprises a length of an optical f ibre bent into the shape of an arch. Each optical means 2 in Figure 2 would thereby be replaced with one length of a fibre. A problem with the use of optical fibres is, however, that their smallest allowable bending radius is relatively large, wherefore they require relatively plenty of space in the direction of height of the paper transfer passage. In addition, they are difficult to install with sufficient accuracy.

Figure 2 shows an arrangement utilizing the procedure according to the invention to detect whether the document is at right angles. When it is to be detected whether the document is at right angles to the longitudinal direction of the paper transfer passage, two detectors positioned on a line transverse to the paper transfer passage are typically used. If the feeding of the document is possible substantially at any transverse position of the paper transfer passage, it is necessary to provide several such pairs of detectors in the transverse direction of the paper transfer passage. A solution to this problem is shown in Figure 2, in which the light propagation between photoemitter and photodetector pairs U1, Q1 and U2, Q2, respectively, is controlled similarly as in connection with the embodiment of Figure 1. The light propagation is thus controlled by means of optical means 4 so that the light is passed several times across the paper transfer passage 1 from points spaced from each other in the transverse direction of the passage. As there are two signals that are transmitted and received in this way, the 8 optical means 4 have to be designed f rom the viewpoint of the propagation of the two signals. Therefore they comprise two light inlets 5 and 6 and two light outlets 7 and 8, respectively. A signal transmitted by the photoemitter Ul in the embodiment of Figure 2 enters the prism through the inlet 5 and is then refracted within the prism 4 so that it leaves the prism through the outlet 7. Correspondingly, a signal transmitted by the photoemitter U2 enters the prism 4 through the inlet 6 and leaves it through the outlet 8. As appears from Figure 2, the signal paths may cross, which, however, is not problematic due to the nature of light.

The manufacture of the optical means used in the embodiment shown in Figure 2 has the same advantages offered by the series production of plastic bodies as the manufacture of the optical means 2 shown in Figure 1. Accordingly, the cost of the embodiment of Figure 2 will be very low.

Figure 3 shows an alternative to the optical means 4 of Figure 2. The alternative optical means shown in Figure 3 comprises two lengths of an optical fibre bent into the shape of an arch and positioned so as to overlap each other, so that the light propagation paths also overlap. The structure shown in Figure 3 has the same problems as the single length of an optical fibre mentioned above.

Typically, the photoemitters are LEDs emitting infrared light, but they could also comprise com- ponents emitting light of some other type; in the embodiment of Figure 2, a single large-area photoemitter emitting two light signals, through the openings of the optical mask 9 could also be used. The photodetectors, in turn, are preferably phototransistors. It is, however, to be understood that 9 the nature of the photoemitters and photodetectors may differ from that described above; in fact, the use of all conventional photosensitive components is possible in the printer according to the invention, provided that they are applied in such a way as is specific to these components either for transmitting light or receiving light. As to the operation of the embodiment of Figure 2, it is also to be noted that the signals from the photodetectors Q1 and Q2 are connected in a conventional manner to a logic means which detects when both signals are in a state indicating that a document has been fed into the paper transfer passage. In such a case, it is known that the document' is at right angles to the paper transfer passage when the detectors are positioned right at the back edge guide of the document.

A printer or a similar output device according to the invention, and especially a means provided in it for detecting whether a document is present or whether it is at right angles, has been described above only by means of certain exemplifying embodiments, and it is to be understood that several modifications are possible in the structural arrangements described above without, however, deviating from the scope of protection defined in the attached claims.

Claims

Claims:

1. A printer or a similar output device for producing characters on a document f ed into a paper transfer passage (1) of the device, comprising at least one means provided in connection with the paper transfer passage for detecting the document, said means comprising a photoemitter (U1) and a photodetector (Q1) positioned in the paper transfer passage (1) so that a document fed to a light propagation path between the photoemitter (U1) and the photodetector (Q1) causes a change in the amount of light received by the photodetector (Q1), c h a ra c t e r i z e d in that optical means (2; 3) are provided on the light propagation path between the photoemitter (U1) and the photodetector (Q1)", said optical means (2; 3) being positioned on the opposite surfaces of the paper transfer passage with a mutual spacing in the transverse direction of the paper transfer passage (1) so as to cause the light to pass several times across the paper transfer passage before it falls on the photodetector (Q1).

2. A printer or a similar output device for producing characters on a document fed into a paper transfer passage (1) of the device, comprising at least one means provided in connection with the paper transfer passage for detecting whether the document is at right angles to the paper transfer passage, said means comprising at least one source of light (U1, U2) and two photodetectors (Q1, Q2) positioned on the same line perpendicular to the paper transfer passage, the photodetectors being positioned along the paper transfer passage (1) so that a document fed to light propagation paths between the photo- emitter(s) (U1, U2) and the photodetectors (Q1, Q2) 11 at right angles to the paper transfer passage causes a change in the amount of light received by the two photodetectors (Ql, Q2), c h a r a c t e r i z e d in that optical means (2; 3; 4) are provided on the light propagation paths between the photoemitter(s) (Ul, U2) and the photodetectors (Ql, Q2), said optical means being positioned on the opposite sur faces of the paper transfer passage so as to cause the light to pass several times across the paper transfer passage before it falls on the photodetectors (Ql, Q2).

3. A printer or a similar output device according to claim 1 or 2, characterized in that the optical means comprises a prism (2) for diverting the light beam so that it is again passed across the paper transfer passage from a point spaced from the inlet point in the transverse direction of the paper transfer passage.

4. A printer or a similar output device accord- ing to claim 1 or 2, characterized in that the optical means comprises a length (3) of an optical fibre bent into the shape of an arch for diverting the light beam so that it is again passed across the paper transfer passage from a point spaced from the inlet point in the transverse direction of the paper transfer passage.

5. A printer or a similar output device according to claim 2, c h a r a c t e r i z e d in that the optical means is a prism (4) comprising two light inlets (5, 6) and two light outlets (7, 8), thus forming part of both light propagation paths.

6. A printer substantially as-hereinbefore described with reference to Figures 1 and 2 or to Figures 2 and 3 of the accompanying drawings.